Basically there are some things you can do in C# and VB.net that means
other languages may not be able to inherit the code and/or consume it properly.

For example C# supports unsigned INTs which are not a type that all .net
languages are guaranteed to support. If one used them as parameters to a
function a language like VB.net or Perl.net could not call that function.

If the unsigned INT happened inside the function any language could call
that function but if it appeared as parameter/signature a language that
could not construct an unsigned INT would have trouble calling it.

Same thing with Case Sensitive methods in C#

C# could call a DoTask() or doTask() method and would be calling 2 distinct
methods because their are 2 separate mothods case-sensitivity is what makes
them different.

If VB.net called the function Dotask or any of the capitalization variants
it would be ambigous which to call so we would call the C# class with case
sensitive methods "NOT CLS compliant".

C# and VB.net compilers have switches to check for CLS compliant and warn
if violated.


There are other good practices besides CLS compliance that FXCOP can catch.....
http://www.gotdotnet.com/team/libraries/
Just because code works and is fast enough does not ensure it is
written the best way.